Cerebral blood flow (CBF) defines the rate of delivery of metabolic substrates and is central to brain metabolism. A non-invasive method for measuring regional cerebral blood flow is therefore important for assessing pathologies associated with alterations in cerebral metabolism such as carotid artery stenosis, stroke, and brain tumors, as well as for studying mental illnesses and drug abuse. In this study we will develop and assess the feasibility of a novel MR hardware for regional CBF and perfusion territory mapping in humans. The novel Arterial Spin Labeling (ASL) technique for cerebral perfusion and perfusion territory mapping proposed will build on our preliminary MR continuous Arterial Spin Labeling (cASL) work which has provided the first system capable of performing cASL in humans at 3T. To achieve this, we will validate the feasibility of a method employing a separately gated OW AF source that can be flexibly interfaced to GE or Siemens scanners and an independently detunable spin-labeling coil to magnetically label inflowing blood water for use in conjunction with a detunable head coil to eliminate interactions between the imaging and labeling systems. The proposed system will improve the MR perfusion measurements by: 1) Providing a magnetization transfer-free technique allowing the acquisition of multi-slice, arbitrary plane, quantitative MR perfusion maps. 2) Improving sensitivity and coverage by covering all of the major arteries with an efficient labeling coil, thus enabling a multi-coil cASL method that will label both posterior and anterior circulation at 3T. Continuous ASL methods has previously been limited to 1 .5T by potentially unsafe RF power demands. 3) Independently labeling each of the carotid arteries to allow the mapping of their perfusion territory and assessing collateral flow. PROPOSED COMMERCIAL APPLICATION: Cerebral perfusion measurements by MRI are a relatively new but rapidly growing method for studying a wide range of disorders that alter local or global cerebral blood flow. We plan to make the two coil arterial spin labeling system available for the first time, to the over 200 neuroimaging research sites. We plan to pursue a clinical product based on the success of the "investigational use only" device.